Floyd County Cambrian: Any clues?

[David Schwimmer]

14 hours ago, Spongy Joe said:

Thanks for adding those links, Doushantuo!

 

I'm going to try to be restrained here. Schwimmer & Montante's work on the Conasauga stuff doesn't fill me with a warm, fuzzy feeling. The last link, to the presentation, is actually pretty informative... but not in the way he might like. Trying to call those little spherical 'sponges' Eiffelia globosa shows a substantial failure of understanding as regards what Eiffelia is actually like, irrespective of interpretations. The one with 'possible surface expression of spicules' can only work if it had completely different spicules (and arrangement) to Eiffelia, for example. You can't recognise Eiffelia globosa purely on the basis of globosity. It just ain't so!

    Some of the other bits are dodgy too (that "arthropod appendage"... hmm...), but the sponges take the biscuit entirely.

 

The 'spicule' evidence is also really unconvincing. The main problem is that it's very easy to see cross-shaped structures, or even just lines, and say you've found spicules. One of the classics were the ones described by none other than Martin Brasier (et al., 1997, image below) that held the record as the earliest reliable Precambrian sponge remains... before they turned out to be arsenopyrite crystals when re-examined twenty years later. Don't believe that there are spicules just because someone claims it and shows a low-res image... 

 

And this, of course, is why Brooksella is still such a delicious controversy, all those years after it was first discovered. It probably is a concretion growing around a trace fossil, but the waters have been so muddied by other claims that nobody's sure of anything any more!

 

Well, in fairness, warm/fuzziness isn't part of technical work.  You will notice there was a ? after the Eiffelia ID in the 2007 paper. However, we have more than 2 dozen specimens of the same morphology with an unmistakable osculum and globe shape. There is no trace fossil or organism known with that shape, other than Eiffelia.  It was a good tentative ID.

 The filamentous appendages in the Glyphaspis specimen are very clear, both in form and location, even more so when the specimen was discovered; unfortunately, it had to be coated to prevent cracking, and some of the relief was lost. None of my Cambrian colleagues have questioned that ID.

Cheers.

Edited May 12, 2018 by David Schwimmer
typos

[David Schwimmer]

1 hour ago, FossilDAWG said:

Hey, David Schwimmer is in the house!   Welcome to the Fossil Forum!  Your input will certainly be appreciated.

I can't say if the trilobite is a molt or dead individual, as it is upside down (relative to the Brooksella surface).  All that can be seen is the entire ventral edge of the pygidium, thorax, and cephalon, so you can see the outline of the trilobite, but it all appears to be fully articulated.  To uncover the dorsal surface I would have to destroy the Brooksella, which would be exceedingly counterproductive, and anyway I have had no luck "prepping" trilobites from inside the silica nodules.  I may try to have a CT scan done to see if we can image the trilobite inside the Brooksella.

 

Cheers,

Don

A quick way to tell is whether or not the librigenae are attached. That would suggest a dead individual in a ptychopariid. If absent, almost certainly a molt. If present, it might suggest dead.

[Spongy Joe]

2 minutes ago, David Schwimmer said:

Well, in fairness, warm/fuzziness isn't part of technical work.  You will notice there was a ? after the Eiffelia ID in the 2007 paper. However, we have more than 2 dozen specimens of the same morphology with an unmistakable osculum and globe shape. There is no trace fossil or organism known with that shape, other than Eiffelia.  It was a good tentative ID.

 The filamentous appendages in the Glyphaspis specimen are very clear, both in foerm and location, even more so when the specimen was discovered; unfortunately, it had to be coated to prevent cracking, and some of the relief was lost. None of my Cambrian colleagues has questioned that ID.

Cheers.

Eiffelia was an extremely thin-walled, delicate sponge with large distinctive spicules surrounded by filamentous soft tissues; nothing about it was fused or rigid. Your structures have a hole at one end, with a cylindrical central cavity (that seems to go all the way through..? If so, that's not like any sponge at all, and suggests concretions growing around burrows). That just isn't the morphology of Eiffella, which can't be preserved in the manner illustrated. Many other (usually later) sponges, like Porosphaera, do show a more similar morphology, including thick walls with a partial axial cavity, but I'm afraid Eiffelia doesn't.

 

For the arthropod appendage, I was referring to the one illustrated in that presentation above - which definitely makes me suspicious. The filamentous appendages in Glyphaspis I'm not sure about either way, personally - I have seen similar wrinkling in asaphid trilobite cuticles in Wales, but of course I haven't looked at your specimen and am willing to allow that there was more info there before coating. The naraoid I have no problem with. 

[David Schwimmer]

9 minutes ago, David Schwimmer said:

Well, in fairness, warm/fuzziness isn't part of technical work.  You will notice there was a ? after the Eiffelia ID in the 2007 paper. However, we have more than 2 dozen specimens of the same morphology with an unmistakable osculum and globe shape. There is no trace fossil or organism known with that shape, other than Eiffelia.  It was a good tentative ID.

 The filamentous appendages in the Glyphaspis specimen are very clear, both in form and location, even more so when the specimen was discovered; unfortunately, it had to be coated to prevent cracking, and some of the relief was lost. None of my Cambrian colleagues have questioned that ID.

Cheers.

Also, on the "sponginess" of "Brooksella," first, I have specimens with marginal oscula that seem to be just openings, but I will double check on that back in the lab.  Also, assuming these Cambrian things are just that, an ancient group, it is not parsimonious to assume they had the same morphology as later sponges. I've seen a lot of variability among sponges, and as with most taxa, no single (or even several) morphology is invariant. I was initially curious about the rarity of preserved axons, but the Conasauga nodules are odd and seem to represent a fairly novel sedimentary situation. As I noted, we find these things in all manner of shapes and sedimentary situations. I assume the spicules became part of the silica that became the enclosing material. Still some unknowns.

[Spongy Joe]

Hi David,

    Great that you'll check on the possibility of some of those structures being osculum-like - that will certainly help, although you still have the problem that some of them, at least, don't seem to be.

    As for the early sponges, you might be surprised to learn that morphological variability is a derived trait. The earliest members of each class (and the things I've been interpreting for years as stem groups) are much more genetically constrained in morphology. Few Cambrian sponges are anything like as variable as this thing is.

    It's certainly not a given that early sponges were structurally the same as modern ones, but of course that's why we study them. Follow the morphologies backward in time, and you see what is shared and plesiomorphic and what is derived. A single axis, radial/tetraradial symmetry and a thin skeletal wall surrounding a hollow interior are plesiomorphic. All the rest, including lobate and compound structures, are modifications of this basic bauplan.

    Anyhow, it's Saturday, and I'm off for a walk in the park before the Nanjing summer makes that unbearable!

Will look forward to continuing this later... but really, it's not a sponge.

[Nimravis]

David,

 

 Thanks for chiming in on this discussion, I thought that you would be interested in this. 

 

Ralph

[MeargleSchmeargl]

 

 

Origin debates aside, where can I get my hands on some in GA? I heard near Rome on the Coosa is a good spot for them.

[Tidgy's Dad]

Great thread! 

This reasoned intelligent debate is fascinating and worthwhile.

This sort of topic will likely inspire further research on Brooksella and so we may get closer to a solution. 

Wonderful!